I keep hearing from various peoples that not eating enough calories in a day will cause the body to "shut down" fat burning and possibly start tapping the muscles for calories. Is this true? What damage can a 24hr fast do?

I keep hearing from various peoples that not eating enough calories in a day will cause the body to "shut down" fat burning and possibly start tapping the muscles for calories. Is this true? What damage can a 24hr fast do?

How do you define, "not enough calories"? Obviously to lose weight you need to burn more calories than you eat. But there's a difference between running a daily calorie deficit and fasting.

From what I have read, fasting will cause your body to go into "starvation mode", where the metabolism slows down dramatically. But where did you hear that fat burning would stop during a fast? Fat is a great energy source, much more so than protein, so that doesn't make sense.

Anyway, why do you want to fast? If you want to lose weight, fasting is not the answer. If anything, to lose weight you should eat more meals, not fewer, while still maintaining a calorie deficit.

Other than temporarily slowing your metabolism, I'm not sure what "damage" a 24-hour fast can do. I doubt it can harm you too much. But what are the benefits of fasting? I'm skeptical that there are any.

bock

What you've heard is true, but one day of fasting is not going to cause any damage.

I keep hearing from various peoples that not eating enough calories in a day will cause the body to "shut down" fat burning and possibly start tapping the muscles for calories. Is this true? What damage can a 24hr fast do?

I don't think that you will do any damage by fasting for 24 hours but you are just going to shut down your metabolism. When you start eating again your metabolism will take a while to get going again so you are essentially going to burn fewer calories.
The best thing would be to get your metabolism reved up to burn more calories throughout the day and when sleeping. There are probably many ways to do this but here are a couple. Build muscle. Muscle needs more calories than fat. Spread your calories throughout the day. Eat 5 or 6 small meals rather than 3 large meals. Exercise after you eat. Do an easy bike ride or fast paced walk for 40 minutes after breakfast and 20 minute easy bike ride or fast paced walk after lunch. If I am doing a hard training day, I try to do it before I go to work or just before supper. It's pretty tough to get a hard exercise in first thing in the morning.
Your body will tap into your muscles for nutrients if you are losing the weight to fast so aim for about 1-2 pounds per week. Good Luck!

Healthcrazy

Fasting will probably just make you obsess about food even more. (At least it would me ;) ) I'm using the South Beach Diet to carve off the winter fat but adding in carbs from whole grains instead of going strictly Lo-carb. As an athlete you gotta replenish the stores. Anyhoo, don't hurt yourself. Like the others say. Eat lots of small, healthy meals and keep riding.

I keep hearing from various peoples that not eating enough calories in a day will cause the body to "shut down" fat burning and possibly start tapping the muscles for calories. Is this true? What damage can a 24hr fast do?

I think that is inaccurate. The longer you've been fasting the greater the percentage of calories burned will be from fat. Although you may be burning fewer absolute calories because your metabolism slows down. If anything during prolonged fasting protein would be burned to produce ketones to supply the brain and red blood cells with energy because these tissues can not rely on fat for energy. Normally they rely on carbohydrates but when fasting the bodies stores of carbs are depleted rapidly thus necessitating ketone production.

I fast for spirtual reasons every so often. And obsessing about food - yes, it's not an easy thing to do, you put your focus elsewhere (prayer) whenever that "obsession" creaps up. I know it sounds kinda nutzo and "on the edge" - but it is very rewarding spirtually.

So - In a typical 24 hour fast...you'll be amazed that you might drop 5 pounds. BUT...and here's the big BUT - as mentioned before, your metabolism slows tremendously - pretty much shuts down. Then as you eat over the next few days...and weigh yourself - all of a sudden you're at or OVER the weight you started before the fast.

Here is an AWESOME resource about fasting - SAFELY. They also sell a great book on the subject too. Your body goes through a very predictable cycle throughout a fast, you can plan/prepare for it and fast safely.

http://64.106.220.190/level%202/Fasting%20Page%20Guide.htm

Fasting is NOT for healthy weight loss - especially for an athlete though.

I think that is inaccurate. The longer you've been fasting the greater the percentage of calories burned will be from fat. Although you may be burning fewer absolute calories because your metabolism slows down. If anything during prolonged fasting protein would be burned to produce ketones to supply the brain and red blood cells with energy because these tissues can not rely on fat for energy. Normally they rely on carbohydrates but when fasting the bodies stores of carbs are depleted rapidly thus necessitating ketone production.


Yep. The body strives to conserve lean body mass during starvation, ketones being uniquely able to nourish the brain & vascular system in the absence of glucose. What you said isn't entirely true though, as the brain and red blood cells rely on ketones which, in starvation situations are created when the liver metabolises fatty acids released from adipose tissue. Lean mass will decrease during prolonged starvation, but the body would rather use fatty acids/ketones. The same principle drives the low-carb or "ketogenic" diets that are all the rage.

Either way in a 24 hour fast (assuming you don't build up to it, you go from normal diet to starvation), your body will quickly use up the immediately avialable resources via some hormonal changes (chiefly glucagon. This period is probably the 'tapping the muscles' to which lotus referred) and THEN, a day or so later begin using ketones as the body's chief source of energy. A 24 hour fast is pretty damn safe unless you have an insanely low % body fat or have other health concerns. But don't take my word for it. I'm an EMT and hobbyist but def. NOT a doctor.

Yep. The body strives to conserve lean body mass during starvation, ketones being uniquely able to nourish the brain & vascular system in the absence of glucose. What you said isn't entirely true though, as the brain and red blood cells rely on ketones which, in starvation situations are created when the liver metabolises fatty acids released from adipose tissue. Lean mass will decrease during prolonged starvation, but the body would rather use fatty acids/ketones. The same principle drives the low-carb or "ketogenic" diets that are all the rage.

Either way in a 24 hour fast (assuming you don't build up to it, you go from normal diet to starvation), your body will quickly use up the immediately avialable resources via some hormonal changes (chiefly glucagon. This period is probably the 'tapping the muscles' to which lotus referred) and THEN, a day or so later begin using ketones as the body's chief source of energy. A 24 hour fast is pretty damn safe unless you have an insanely low % body fat or have other health concerns. But don't take my word for it. I'm an EMT and hobbyist but def. NOT a doctor.

Thanks for the correction.

Why are you wanting to fast?
Fasting gives your digestive system a chance to rest, but it does pretty much stop your metabolism . Anything to extreme will just end up hurting you i.e. if you're not careful you'll end up burning muscle instead of fat.
If you do fast, make sure you work up to it like someone said, but also that you ease back off of it.


Just my two cents

Why are you wanting to fast?
Fasting gives your digestive system a chance to rest, but it does pretty much stop your metabolism . Anything to extreme will just end up hurting you i.e. if you're not careful you'll end up burning muscle instead of fat.
If you do fast, make sure you work up to it like someone said, but also that you ease back off of it.


Just my two cents


yeah, you're very right about that... Basically, fasting and normal metabolism are mutually exclusive things. People who fast have their reasons (I've done it before meself), but if you're really hardcore about sticking to a diet and exercise regimen with a desired result with no acceptable leeway in progress, fasting isn't an option.